The present invention, in some embodiments thereof, relates to optical switching and, more particularly, but not exclusively, to switching of optical channels among multiple input and output fibers.
Optical telecommunication employs optical systems for switching, filtering, multiplexing and demultiplexing of optical signals. For example, in wavelength division multiplexing (WDM) telecommunication, multiple optical channels, each having a unique range of wavelengths, carry modulated optical signals in a single optical fiber between a transmitter and a receiver, thereby increasing the transmission capacity of the communication. The transmitter uses an optical multiplexer to combine multiple channels into the fiber for transmission, and the receiver uses an optical demultiplexer to separate the optical channels for detection.
When WDM channels have to be routed at network nodes from one transport fiber to another, it is advantageous to do this routing in an all-optical fashion, i.e., without detecting the signal and retransmitting it. A routing functionality at network nodes is performed by a system called an optical cross-connect system.
One type of optical cross-connect system employs a single large port-count cross-connect that is not wavelength-selective, a demultiplexer and a multiplexer. In operation, the demultiplexer separates the WDM channels, the cross-connect performs the routing and the multiplexer which recombines the WDM channels at their respective rout thereafter.
Another type of optical cross-connect system employs a few wavelength-selective switches (WSS), which either distribute wavelengths from one fiber to multiple output fibers, or combine wavelengths from multiple fibers to a single output fiber. WSS are typically based on switching finite bandwidths of dispersed light, typically with micro-electro-mechanical system (MEMS) micromirrors or with liquid-crystals (LC) Spatial Light Modulators. Such configurations have the advantage that their passbands are typically broader than the solution employing discrete multiplexer and demultiplexer pair, which imply that the WDM channel experiences less filtering effects, thereby reducing cumulative degradation of the signals.
Systems of WSS are known in the art. Typically, such systems employ a combination of a grating and a lens for spatially dispersing or combining the input light, and an array of beam steering elements which performs the switching operation. The spectral characteristics of such systems are generally satisfactory because they switch continuous spectral bands belonging to individual channels [D. M. Marom, et al, 2005, “Wavelength-Selective 1×K Switches using Free-Space. Optics and MEMS Micromirrors: Theory, Design, and Implementation,” IEEE J. Lightwave Technol., Vol. 23, No. 4, pp. 1620-30].
Additional background art includes U.S. Pat. Nos. 7,649,670, 7,333,688, 7,376,311, 7,283,709, 7,231,106, 7,126,250, 7,016,098, 6,984,917, 6,867,920, 6,738,540, 6,097,859, 6,289,145 and 6,327,398.